Stable homotopy over the Steenrod algebra John H. Palmieri In this paper I apply the results of "Axiomatic stable homotopy theory" (Hovey-Palmieri-Strickland) to the study of the Steenrod algebra A and its cohomology Ext_A. To do this, I work in the category Stable(A), in which the objects are cochain complexes of injective comodules over the dual of A. In this category, one can set up basic homotopy theoretic tools (like Postnikov towers); using these, I generalize some well-known results about A-modules to the category Stable(A) (like the vanishing line theorems of Anderson-Davis and Miller-Wilkerson. I then use the methods and philosophy of modern stable homotopy theory to study Stable(A). This gives generalizations of deeper results about A-modules (such as the nilpotence theorems of the author), new proofs of old results (such as "chromatic convergence" in Stable(A)), and new results (such as a disproof of a version of the telescope conjecture in the category Stable(A)).